Cementitious compositions have been used in the construction industry for years. Examples of cementitious compositions include concrete, mortar, grout, and stucco. Stucco is commonly used in the construction of buildings, particularly on the exterior of a building in lieu of vinyl siding. A framework such as paper or metal wire is affixed to a building, for example, and stucco is applied to the framework. Stucco is typically comprised of cement and inert materials such as sand and lime.
A common problem with a cementitious composition such as stucco is that it has a high pH when it is fresh or newly applied. A high pH (e.g., >9) intrinsically protects against microorganisms and will naturally protect the material from attack by fungi and other microorganisms. However, over time, the cementitious composition is gradually neutralized and an untreated cementitious composition loses this innate efficacy against microorganisms such as bacteria, algae, mold and fungus. Furthermore, stucco is porous and absorbs moisture, which is particularly attractive to microorganisms.
Others have attempted to add antimicrobial agents to cementitious compositions and to other components of cementitious compositions such as fibers. However, there are problems that have yet to be solved with known antimicrobial cementitious compositions. For example, the high pH of cementitious compositions places unique demands on the particular choice of an antimicrobial agent. Since the pH of a cured cementitious composition tends to remain very high even after it sets, the particular antimicrobial agent chosen must be very resistant to hydrolysis at the high pH. If the antimicrobial agent is susceptible to hydrolysis, then it would be most likely to be quickly degraded. Some antimicrobial agents such as triclosan are also particularly sensitive to the combination of high pH and ultraviolet light such that the antimicrobial agent causes yellowing when the two conditions are present. For example, U.S. Pat. No. 6,162,845 discloses the use of triclosan in fibers for blending with concrete and like materials.
Another problem with many known antimicrobial agents is that they disrupt the cure chemistry of a cementitious composition. For example, certain antimicrobial agents may be susceptible to coupling with impurities and will lead to possible color changes. Still another problem with many known antimicrobial agents is that they have poor solubility in a cementitious composition. The agents may leach out of the cementitious composition and, also as a result of poor solubility, cannot be homogeneously applied to the substrate.